A power supply that is often used in telecommunications, transportation, industry and other applications may require electrical isolation between an input and an output of the power supply. A transformer with a primary winding and a secondary winding is often used to provide this isolation. Furthermore, the power supply may further include a switching element and a rectifying diode connected to the secondary winding.
FIG. 1 is a diagram which shows a schematic illustration of a power supply and a device for controlling the power supply in the prior art. As shown in FIG. 1, a power supply 100 is used to convert a first voltage (Vin, such as a direct current voltage or direct voltage) into a second voltage (Vo, such as a direct current voltage or direct voltage). The power supply 100 may include a switching element 101, a transformer 102 with a primary winding 1021 and a secondary winding 1022, a rectifying diode 103 connected to the secondary winding 1022.
As shown in FIG. 1, a device 110 for controlling the power supply 100 may include a source voltage terminal 111 (for example it is referred to as VCC), a feedback terminal 112 (for example it is referred to as FB), and a driving terminal 113 (for example it is referred to as DRV) for driving the switching element 101. An on/off operation of the switching element 101 may be controlled by a driving signal from the driving terminal 113 with a pulse width modulation (PWM). Furthermore, COMP denotes a comparing terminal.
As shown in FIG. 1, the device 110 may further include an oscillator 114 configured to output a ramp signal into a driving circuit 115. Furthermore, as shown in FIG. 1, a current signal from an OCP (over current protection) terminal 116 may be compared with a current reference signal (for example it is referred to as REF1) in a first comparator 117. Therefore, a first controlling signal may be outputted from the first comparator 117 into the driving circuit 115; a current being conducted (or may be referred to as passed though or flowed through) in the switching element 101 can be constrained when it is overloaded, such that the switching element 101 can be protected.
As shown in FIG. 1, the feedback terminal 112 may be inputted a feedback signal (such as from a side of the secondary winding 1022). The feedback signal may be compared with a reference signal (for example it is referred to as REF2) in an error amplifier 118, and the compared signals generates a compensating error signal. The compensating error signal outputted from the error amplifier 118 may be compared with the current signal from the OCP terminal 116 in a second comparator 119. Therefore, a second controlling signal may be outputted from the second comparator 119 into the driving circuit 115.
This section introduces aspects that may facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.